Wireless sensor networks are known to be used in process control systems. Examples on such networks are ZigBee and WirelessHart, ISA100, WIA-PA and Bluetooth. There also exist some WLAN based sensor networks.
Another type of network is Wireless Interface for Sensors and Actuators (WISA). Here data is transmitted with error codes in order to determine if data is received correctly or not. Furthermore, in case data is not received correctly then a retransmission may be made.
One cause of a high number of errors is frequency selective fading. Another cause may be by several devices transmitting at the same frequency as a transmitting unit and may cause a loss of data packets.
One way to address this problem, which is described in WO 2005/067161 is fast frequency hopping. In fast frequency hopping a bit is divided into a number of segments, where each segment is transmitted with a different frequency. Through using frequency hopping it is then possible to lower the number of faulty bits. As several frequencies are used for the same bit, it is thus ensured that even if one frequency is bad and one segment of a bit is received with poor quality, then another segment of the same bit is normally received properly with adequate quality and hence the bit is received correctly.
There is the possibility that different devices simultaneously transmit segments with the same frequency. However, if they have different transmission schemes, this will often only happen rarely.
There may be more than one wireless network in the same area and theses network may also interfere with each other. There may for instance be a Wireless Local Area Network (WLAN) in the same are as a WISA network. A WLAN network normally only uses the same frequency. This frequency may have a serious influence on the bit error rate of the WISA system.
It would therefore be of interest to improve upon this situation.